Grammatical errors and spelling errors in business communications REALLY get my goat!! If I receive correspondence from a company with a spelling error, they will certainly not be getting MY business.
At my last company, I was in charge of the hiring of new employees. If I received a resume with spelling or punctuation errors, I didn't even look at it further..into the garbage it went. That may seem harsh but you have to assume that if they aren't even motivated enough to double and triple check their resume, which reflects on them, what type of effort are they going to put into work which reflects on the company...?
Have any of you read "Eats, Shoots and Leaves?" I can't remember the author's name right now. It's a great read, very entertaining!

BTW, there is a store on the corner of my street called "the Trhift Shop." Needless to say, I haven't been in to browse